Positive electrode material and sodium ion battery

Abstract

A positive electrode material. The molecular formula is Na1-naAn+ a[TmbM1 cM2 d]O2, wherein A is one or more alkali metal or alkaline earth metal elements of which the feed property ψA satisfies 0.9ψNa≤ψA≤ψNa; Tm is a combination of one or more elements of Fe, Mn and Co with Ni; M1 is one or more metal elements of which the feed property ψM1 <sp / > is greater than ψ0.6Tmmax; M2 is one or more metal elements of which the feed property ψ0.6M2 <sp / > is greater than ψ0.6Tmmax; and 0<a≤0.1, 0.3≤b<1, 0<c≤0.6, 0≤d≤0.2, b+c+d=1, and values of a, b, c and d enable the positive electrode material to keep charge balance. According to the positive electrode material, the multi-element co-doping of a sodium layer and transition metal layers synergistically enhances the interaction between adjacent transition metal layers, thereby improving the structural stability of the positive electrode material having a large sodium removal amount.

Description

Cathode materials and sodium-ion batteries

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 31, 2023, with application number 202310961005.X and application name “Positive Electrode Materials and Sodium Ion Batteries”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to the technical field of sodium ion batteries, and in particular to a positive electrode material and a sodium ion battery. Background Art

[0003] Due to the shortage of lithium resources and their uneven distribution around the world, the cost of using lithium-ion batteries is too high, which seriously restricts the large-scale use of lithium-ion batteries. Sodium resources are widely distributed, low-cost, and have similar physical and chemical properties to lithium. Therefore, sodium-ion batteries are considered to be the most promising and viable alternative to lithium-ion batteries. Layered transition metal oxides are based on reversible intercalation reactions, have simple synthesis methods and relatively high capacity, and are considered to be the most promising sodium battery positive electrode route for industrialization. However, layered positive electrode materials undergo irreversible phase changes during high-voltage cycling, which makes it difficult to ensure the long cycle life of such materials, which is not conducive to actual commercial application. Therefore, there is an urgent need to find a class of sodium-ion battery positive electrode materials with high reversible specific capacity and stable structure.

[0004] Summary of the Invention

[0005] In view of this, an embodiment of the present application provides a positive electrode material for a sodium ion battery. The positive electrode material rationally designs the doping elements of the sodium layer and the transition metal layer based on the feed property. By co-doping the sodium layer and the transition metal layer with multiple elements, the interaction between O-Na(A)-O between adjacent transition metal layers is synergistically enhanced, thereby suppressing the adverse phase change of the positive electrode material under high pressure, i.e., when highly de-sodiumized, and improving the structural stability of the positive electrode material at a high de-sodiumization amount.

[0006] The first aspect of the embodiment of the present application provides a positive electrode material, the molecular formula of which is Na 1-na A n+ a [Tm b M 1 c M 2 d ]O2, wherein A is one or more alkali metal or alkaline earth metal elements with a power feeding property ψA satisfying 0.9ψNa≤ψA<ψNa; Tm is a combination of one or more elements of Fe, Mn, Co and Ni, M 1 is the feeding characteristic ψM 1 Satisfy ψM 1 >ψ0.6 Tm max One or more metal elements, and M 1 M is an inert element that does not provide charge compensation. 2 is the feeding characteristic ψ 0.6 M 2 Satisfy ψ 0.6 M 2 >ψ 0.6 Tm max One or more metal elements, and M 2 An active element that provides charge compensation; 0<a≤0.1, 0.3≤b<1, 0<c≤0.6, 0≤d≤0.2, b+c+d=1, and the values ​​of a, b, c, and d are such that the positive electrode material maintains charge balance;

[0007] Among them, ψA=χO-χA, ψM 1 =χO-χM 1 , χO is the effective electronegativity of O, χA is the effective electronegativity of A, χM 1 M 1 The effective electronegativity of 0.6 Tm max is the maximum chargeability of Tm when the amount of sodium removed from the positive electrode material is greater than or equal to 0.6, where ψ 0.6 Tm=ψiniTm-0.6*(ψiniTm-ψendTm), ψiniTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 0, and ψendTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 1; ψ 0.6 M 2 =ψiniM 2 -0.6*(ψiniM 2 -ψendM 2 ), ψiniM 2 M is when the amount of sodium removed from the positive electrode material is 0 2 Feeding property, ψendM 2 When the amount of sodium removed from the positive electrode material is 1, M 2 The feedability.

[0008] In the embodiment of the present application, the A replaces the Na site to achieve sodium layer doping, and the M 1 、M 2 Replace the Tm site to achieve transition metal layer doping. 1 As an electrochemically inert element, it cannot provide charge compensation and its charge feeding property remains unchanged during the entire sodium removal process. 2 As an active electrode, the feeding property decreases with the increase of sodium removal. 2 The feedability is limited to the feedability ψ under 0.6 0.6 M 2Make a comparison.

[0009] The positive electrode material of the embodiment of the present application is a layered positive electrode material that can be used as a positive electrode material for sodium ion batteries. The positive electrode material is rationally designed for the doping elements of the sodium layer and the transition metal layer based on the feedability. By co-doping the sodium layer and the transition metal layer with multiple elements, the interlayer force of the adjacent transition metal TM layer is synergistically enhanced, that is, the O-Na-O force, thereby suppressing the adverse phase change of the positive electrode material under high pressure, that is, when highly de-sodiumized, and improving the structural stability of the positive electrode material at high de-sodiumization. Specifically, starting from the electrostatic attraction, the O-Na(A) force is regulated by both the sodium layer and the transition metal layer. On the one hand, the transition metal layer is doped with the element M 1 、M 2 The feedability is as large as possible ψM 1 >ψ 0.6 Tm max , ψ 0.6 M 2 >ψ 0.6 Tm max In the MO-Na(A) structural unit, an electron-donating effect is exhibited on O, thereby increasing the electron cloud density of O and enhancing the O-Na interaction; on the other hand, the electron-donating property of the sodium layer doping element A is as small as possible, 0.9ψNa≤ψA<ψNa, and an electron-pulling effect is exhibited on O, thereby enhancing the O-Na related interaction; under the "one-donating and one-pulling" synergistic effect of the sodium layer and the transition metal layer doping, the O-Na interaction is significantly improved, thereby having a more obvious synergistic inhibitory effect on the slip of the transition metal layer under high pressure. The positive electrode material of the embodiment of the present application can regulate the structural stability of the sodium positive electrode phase through multi-ion synergistic doping without reducing the electrochemically active electrode couple as much as possible, thereby inhibiting phenomena such as layer slip and layer collapse under high pressure.

[0010] In this application, the effective electronegativity of A is χA,M 1 The effective electronegativity χM 1 It can be calculated using the following formula or obtained through query.

[0011] Among them, n * For element M n+ The effective principal quantum number of

[0012] Among them, I m For element M n+ The n-level ionization energy;

[0013] Where R is the Rydberg constant, R = 13.6 eV;

[0014] Among them, r M For element M n+ The coordination radius.

[0015] In this application, ψ 0.6 Tm max It depends on the type of Tm selected in the positive electrode material. For example, when Tm includes Ni, Fe, Mn and Co at the same time, ψ 0.6 Tm max =(ψ 0.6 Fe,ψ 0.6 Mn,ψ 0.6 Co,ψ 0.6 Ni) max , due to calculation, we know that ψ 0.6 Fe=1.698,ψ 0.6 Mn=1.657,ψ 0.6 Co=1.590,ψ 0.6 Ni=1.540, so ψ 0.6 Tm max =1.698. Similarly, when Tm includes Ni, Mn and Co, ψ 0.6 Tm max =(ψ 0.6 Mn,ψ 0.6 Co,ψ 0.6 Ni) max , ψ 0.6 Tm max =1.657. Similarly, when Tm includes Ni, Mn and Fe, ψ 0.6 Tm max =(ψ 0.6 Fe,ψ 0.6 Mn,ψ 0.6 Ni) max , ψ 0.6 Tm max =1.698. Similarly, when Tm includes both Ni and Mn, ψ 0.6 Tm max =(ψ 0.6 Mn,ψ 0.6 Ni) max , ψ 0.6 M max =1.657. Among them, ψ0.6Tm=ψiniTm-0.6*(ψini-ψend), where ψiniTm refers to the power feeding property when the amount of sodium removal of the positive electrode material is 0, and ψendTm refers to the power feeding property when the amount of sodium removal of the positive electrode material is 1.

[0016] In the embodiments of the present application, sodium and oxygen form a sodium layer, and the doping element A is one or more alkali metals or alkaline earth metal elements with a charge-feeding property ψA satisfying 0.9ψNa≤ψA<ψNa. The doping element A replaces the Na site of the sodium layer in the positive electrode material, forming a partial OA structure in the sodium layer. The value of a represents the doping amount of the doping element A. In the present application, 0<a≤0.1. In some embodiments of the present application, 0.01≤a≤0.06. The incorporation of an appropriate amount of doping element A into the sodium layer can, on the one hand, better exhibit an electron-withdrawing effect on the O in the positive electrode material, thereby enhancing the O-Na(A) interaction and improving the structural stability of the positive electrode material under high voltage; on the other hand, it can avoid the occurrence of impurities or element segregation during the synthesis of the positive electrode material; and from a capacity perspective, the appropriate doping of the doping element A has less impact on the amount of sodium removal, which can meet the requirement of a maximum sodium removal amount of 0.6 or more for the positive electrode; from a cost perspective, Na is cheaper than other doping elements, and appropriate doping has a higher performance-to-efficiency ratio.

[0017] In embodiments of the present application, the element Tm is a transition metal layer element, specifically one or more of Ni, Fe, Mn, and Co, and the element Tm and oxygen form a transition metal layer. In some embodiments of the present application, 0.4 ≤ b ≤ 0.9. Controlling the content of the element Tm within a suitable range is beneficial for the positive electrode material to obtain a stable layered structure and maintain characteristics such as high capacity.

[0018] In the embodiment of the present application, M 1 It is an inert element that does not provide charge compensation, that is, it is an electrochemically inactive element. The doping element M 1 Replace the Tm site in the transition metal layer and form part of the M 1 -O structure. The value of c represents M 1 In this application, M 1 It is an inert element, and its doping amount should not be too much, 0<c≤0.6. In some embodiments of the present application, 0.05≤c≤0.2. 1 Controlling the amount of isotope within a suitable range is beneficial to improving the electron cloud density of O through its electron-donating effect on O, thereby enhancing the O-Na interaction, inhibiting high-voltage phase transition, and improving the structural stability of the positive electrode material under high voltage. Moreover, as a material guest doping element, controlling it within a suitable range is beneficial to the synthesis of pure phase materials, avoiding surface segregation caused by insufficient solid solubility, and at the same time can better ensure the capacity of the positive electrode material.

[0019] In the embodiment of the present application, M 2 Active elements that provide charge compensation, that is, electrochemically active elements, doping elements M 2Replace the Tm site in the transition metal layer and form part of the M 2 -O structure. Different from the lithium battery positive electrode, the sodium battery positive electrode has more active electrode candidates. 2 , which is beneficial for example, V, Cr, Cu, Ru, Ir, etc., which have strong electron donating ability to coordinate O under high sodium removal, and can be appropriately introduced to further enhance the interaction force between adjacent Tm layers under high pressure. The value of d represents M 2 In some embodiments of the present application, 0≤d≤0.1. The transition metal Tm layer is doped with element M 2 The amount of Na is controlled within a suitable range. On the one hand, it is beneficial to increase the electron cloud density of O through its electron donating effect on O, thereby enhancing the O-Na interaction and improving the structural stability of the positive electrode material under high voltage. On the other hand, appropriate doping is beneficial to the synthesis of pure phase, and for cost considerations, appropriate doping has a higher performance-efficiency ratio.

[0020] ψNa = 2.416, meaning A can be an element such that 2.174 ≤ ψA < 2.416. In some embodiments of the present application, A is selected from one or more of Li, Mg, Ca, Sr, and Ba. Li, Mg, Ca, Sr, and Ba have lower electron-donating properties than Na. Thus, element A exhibits a stronger electron-withdrawing effect on O than Na, enhancing the O-Na interaction. It is understood that minimizing the electron-donating property of element A is more beneficial for enhancing the O-Na interaction.

[0021] In the embodiment of the present application, ψM 1 >ψ 0.6 Tm max , when Tm includes Ni, Fe, Mn and Co at the same time, ψ 0.6 Tm max =1.698. When Tm includes Ni, Mn and Co, ψ 0.6 Tm max =1.657. In some embodiments of the present application, the M 1 It can be one or more elements selected from Li, Ti, Zn, Mg, Sn, Al, Y, La, Nd, and Zr. 1 With a value greater than ψ 0.6 Tm max The feeding property can make M 1 When the amount of sodium removed from the positive electrode material is x, 0.6≤x≤1, the electron-donating effect on O is greater than that of the original transition metal element Tm, and the coordinated O has a higher electron density, which enhances the O-Na-O interaction force. It can be understood that the element M 1 The feeding property is as large as possible while satisfying the principle of equivalent substitution, which is more conducive to the enhancement of O-Na related effects.

[0022] In the embodiment of the present application, ψ 0.6 M 2 >ψ 0.6 Tm max , the M 2 It can be one or more elements selected from V, Cr, Ru, Cu, and Ir. 0.6 M 2 >ψ 0.6 Tm max Can make M 2 When the amount of sodium removed from the positive electrode material is x, 0.6≤x≤1, the electron-donating effect on O is greater than that of the original transition metal element Tm, and the coordinated O has a higher electron density, which enhances the O-Na-O interaction force. It can be understood that the element M 2 The feeding characteristic ψ 0.6 M 2 As large as possible while satisfying the principle of equivalent substitution is more conducive to the enhancement of O-Na related effects.

[0023] In the embodiment of the present application, the positive electrode material is in the form of spherical, polygonal or lamellar particles with a particle size D50 of 2 μm to 20 μm. A suitable particle size is beneficial for the preparation of positive electrode sheets.

[0024] In the embodiment of the present application, the compaction density of the positive electrode material is 2.8 g·cm -3 -3.2g·cm -3 The higher compaction density of the positive electrode material is beneficial to the improvement of battery capacity.

[0025] In the embodiment of the present application, the 0.2c charging capacity of the positive electrode material is 140 mAh g -1 -180mAh·g -1 The positive electrode material has a high gram capacity, which is beneficial to the improvement of battery capacity.

[0026] In the embodiment of the present application, the crystal structure of the positive electrode material is an α-NaFeO2 hexagonal layered structure. The α-NaFeO2 hexagonal layered structure enables the positive electrode material to have good electrochemical performance.

[0027] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising:

[0028] According to the molecular formula of the positive electrode material Na 1-na A n+ a [M b M 1 c M 2 d ]O2, sodium source, A source, Tm source, M 1 Source, M2 The sources are mixed to obtain a mixture;

[0029] The mixed material is calcined in an oxygen atmosphere to obtain a positive electrode material.

[0030] In the embodiment of the present application, the sodium source includes a sodium-containing compound, and the sodium-containing compound includes one or more of sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide and sodium hydroxide; the A source includes an A-containing compound, and the A-containing compound includes one or more of A-containing carbonates, nitrates, oxides, peroxides, and hydroxides; the Tm source includes a Tm-containing compound, and the Tm-containing compound includes one or more of Tm-containing metal oxides, metal carbonates, metal nitrates, and metal hydroxides; the M 1 Sources include M 1 Compound, the compound containing M 1 Compounds including M 1 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides; the M 2 Sources include M 2 Compound, the compound containing M 2 Compounds including M 2 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides.

[0031] The method for preparing the positive electrode material in the embodiment of the present application has a simple process and does not require complicated steps in the doping process.

[0032] A third aspect of the present invention provides a positive electrode sheet comprising the positive electrode material described in the first aspect of the present invention. The positive electrode sheet prepared using the positive electrode material of the present invention has a high capacity and high structural stability, and can effectively improve the cycling performance of a sodium-ion battery while maintaining its high capacity.

[0033] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector, and the positive electrode active layer includes the positive electrode material.

[0034] The fourth aspect of the embodiment of the present application provides a sodium ion battery, the sodium ion battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet comprises the positive electrode sheet described in the third aspect of the embodiment of the present application. The sodium ion battery of the embodiment of the present application adopts the positive electrode material Na 1-na A n+ a [Tm b M 1 c M 2 d]O2 can effectively improve the cycle performance of sodium-ion batteries while maintaining their high capacity.

[0035] The present application also provides an electrical device, which includes the sodium ion battery described in the fourth aspect of the present application. The electrical device using the sodium ion battery of the present application has high stability.

[0036] In the implementation manner of the present application, the electrical equipment includes electronic equipment, energy storage system, communication equipment or communication base station. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a schematic structural diagram of a positive electrode sheet 10 provided in an embodiment of the present application;

[0038] FIG2 is a schematic structural diagram of a sodium ion battery 100 provided in an embodiment of the present application;

[0039] FIG3 is a schematic structural diagram of an electric device 200 provided in an embodiment of the present application;

[0040] Figure 4 shows the cathode material Na provided in Example 5 of this application. 0.94 Mg 0.03 Ni 0.3 Fe 0.3 Mn 0.3 Li 0.067 Ti 0.133 EDS element distribution map of O2;

[0041] FIG5 is a graph showing the maximum sodium removal amount before phase change of the positive electrode material provided in Example 9 of the present application;

[0042] FIG6 is a phase change capacity curve diagram of the positive electrode material provided in Example 9 of the present application;

[0043] FIG7 is a graph showing the maximum sodium removal amount before phase change of the positive electrode material provided in Comparative Example 7 of the present application;

[0044] FIG8 is a phase change capacity curve diagram of the positive electrode material provided in Comparative Example 7 of the present application. DETAILED DESCRIPTION

[0045] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0046] Sodium layered transition metal oxides are based on reversible intercalation reactions, have simple synthesis methods, and offer relatively high capacity, making them considered the most promising sodium battery cathode route for industrialization. However, due to their structure, the Na interlayer spacing of the P3 phase of sodium layered transition metal oxide cathodes under high pressure is wider than the Li interlayer spacing of lithium battery cathodes, resulting in weaker interaction between adjacent transition metal Tm layers, namely, weaker O-Na-O interaction. When the sodium removal amount reaches 0.6 or above, the O-Na-O interaction is insufficient, and irreversible phase transition caused by Tm layer slip, namely PO phase transition, is prone to occur. As a result, it is difficult to ensure a long cycle life for sodium layered transition metal oxides, which is not conducive to practical commercial application. To solve this technical problem, the present application is designed from the underlying principles without reducing the electrochemically active electrode couple, and the feeding principle is used to screen the doping ions of the sodium layer and the transition metal layer in a targeted manner. A coordinated doping strategy of the sodium layer and the transition metal layer is adopted to modify the existing sodium layered transition metal oxide, maximize the O-Na-O interaction force, enhance the stability of adjacent transition metal layers, inhibit phase change under high pressure and increase the amount of sodium removal before phase change, thereby improving the high-voltage stability of the positive electrode material and enabling the positive electrode material to have a more stable high-capacity performance.

[0047] The present invention provides a positive electrode material, the molecular formula of which is Na 1-na A n+ a [Tm b M 1 c M 2 d ]O2, the positive electrode material is a doped sodium transition metal oxide, wherein A is one or more alkali metal or alkaline earth metal elements with a feeding property ψA satisfying 0.9ψNa≤ψA<ψNa, and A replaces the Na site; Tm is a combination of one or more elements of Fe, Mn, Co and Ni, M 1 is the feeding characteristic ψM 1 Satisfy ψM 1 >ψ 0.6 Tm max One or more metal elements, and M 1 M is an inert element that does not provide charge compensation. 2 is the feeding characteristic ψ 0.6 M 2 Satisfy ψ 0.6 M 2 >ψ 0.6 Tm max One or more metal elements, and M 2 To provide active elements for charge compensation, M 1 、M 2Replace the Tm site; 0<a≤0.1, 0.3≤b<1, 0<c≤0.6, 0≤d≤0.2, b+c+d=1, and the values ​​of a, b, c, and d are such that the positive electrode material maintains charge balance;

[0048] Among them, ψA=χO-χA, ψM 1 =χO-χM 1 , χO is the effective electronegativity of O, χA is the effective electronegativity of A, χM 1 M 1 The effective electronegativity of 0.6 Tm max is the maximum charge capacity of Tm when the amount of sodium removed from the positive electrode material is greater than or equal to 0.6, where ψ 0.6 Tm=ψiniTm-0.6*(ψiniTm-ψendTm), ψiniTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 0, and ψendTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 1; 0.6 M 2 =ψiniM 2 -0.6*(ψiniM 2 -ψendM 2 ), ψiniM 2 M is when the amount of sodium removed from the positive electrode material is 0 2 Feeding property, ψendM 2 When the amount of sodium removed from the positive electrode material is 1, M 2 The feedability.

[0049] In this application, M 1 As an electrochemically inert element, it cannot provide charge compensation and its charge feeding property remains unchanged during the entire sodium removal process. 2 As an active electrode, the feeding property decreases with the increase of sodium removal. 2 The feedability is limited to the feedability ψ under 0.6 0.6 M 2 χO and χA are fixed values ​​that can be obtained by looking up the table.

[0050] The positive electrode material of the embodiment of the present application is a layered positive electrode material that can be used as a positive electrode material for sodium ion batteries. The positive electrode material is rationally designed for the doping elements of the sodium layer and the transition metal layer based on the feedability. By co-doping the sodium layer and the transition metal layer with multiple elements, the interlayer force of the adjacent transition metal TM layer is synergistically enhanced, that is, the O-Na-O force, thereby suppressing the adverse phase change of the positive electrode material under high pressure, that is, when highly de-sodiumized, and improving the structural stability of the positive electrode material at high de-sodiumization. Specifically, starting from the electrostatic attraction, the O-Na(A) force is regulated by both the sodium layer and the transition metal layer. On the one hand, the transition metal layer is doped with the element M 1 、M 2The feedability is as large as possible ψM 1 >ψ 0.6 Tm max , ψ 0.6 M 2 >ψ 0.6 Tm max In the MO-Na(A) structural unit, an electron-donating effect is exhibited on O, thereby increasing the electron cloud density of O and enhancing the O-Na interaction; on the other hand, the electron-donating property of the sodium layer doping element A is as small as possible, 0.9ψNa≤ψA<ψNa, and an electron-pulling effect is exhibited on O, thereby enhancing the O-Na related interaction; under the "one-donating and one-pulling" synergistic effect of the sodium layer and the transition metal layer doping, the O-Na interaction is significantly improved, thereby having a more obvious synergistic inhibitory effect on the slip of the transition metal layer under high pressure. The positive electrode material of the embodiment of the present application can regulate the structural stability of the sodium positive electrode phase through multi-ion synergistic doping without reducing the electrochemically active electrode couple as much as possible, thereby inhibiting phenomena such as layer slip and layer collapse under high pressure.

[0051] In this application, the effective electronegativity of A is χA,M 1 The effective electronegativity χM 1 It can be calculated using the following formula:

[0052] Among them, n * For element M n+ The effective principal quantum number of

[0053] Among them, I m For element M n+ The n-level ionization energy;

[0054] Where R is the Rydberg constant, R = 13.6 eV;

[0055] Among them, r M For element M n+ The coordination radius.

[0056] In this application, ψ 0.6 Tm max It depends on the type of Tm selected in the positive electrode material. For example, when Tm includes Ni, Fe, Mn and Co at the same time, ψ 0.6 Tm max =(ψ 0.6 Fe,ψ 0.6 Mn,ψ 0.6 Co,ψ 0.6 Ni) max , due to calculation, we know that ψ 0.6 Fe=1.698,ψ 0.6 Mn=1.657,ψ0.6 Co=1.590,ψ 0.6 Ni=1.540, so ψ 0.6 Tm max =1.698. Similarly, when Tm includes Ni, Mn and Co, ψ 0.6 Tm max =(ψ 0.6 Mn,ψ 0.6 Co,ψ 0.6 Ni) max , ψ 0.6 Tm max =1.657. Similarly, when Tm includes Ni, Mn and Fe, ψ 0.6 Tm max =(ψ 0.6 Fe,ψ 0.6 Mn,ψ 0.6 Ni) max , ψ 0.6 Tm max =1.698. Similarly, when Tm includes both Ni and Mn, ψ 0.6 Tm max =(ψ 0.6 Mn,ψ 0.6 Ni) max , ψ 0.6 M max =1.657. Among them, ψ0.6Tm=ψiniTm-0.6*(ψini-ψend), where ψiniTm refers to the power feeding property when the amount of sodium removal of the positive electrode material is 0, and ψendTm refers to the power feeding property when the amount of sodium removal of the positive electrode material is 1.

[0057] In the embodiment of the present application, the sodium element and the oxygen element form a sodium layer, and the doping element A is one or more alkali metals or alkaline earth metal elements whose feeding property ψA satisfies 0.9ψNa≤ψA<ψNa. The doping element A replaces the Na site of the sodium layer in the positive electrode material and forms a partial OA structure in the sodium layer. ψNa=2.416, 0.9ψNa=2.174, that is, A can be an element with 2.174≤ψA<2.416. In the layered positive electrode material, the sodium layer and the transition metal Tm layer are arranged alternately. Selecting an alkali metal or alkaline earth metal with suitable feeding properties to dope the sodium layer is beneficial to avoid the problem of metal elements that do not match the coordination octahedron of the sodium layer being doped into the sodium layer, causing significant damage to the coordination environment of the sodium layer, thereby better maintaining the original crystal structure of the sodium layer.

[0058] In some embodiments of the present application, A is selected from one or more elements selected from Li, Mg, Ca, Sr, and Ba. ψLi = 2.413, ψMg = 2.206, ψCa = 2.280, ψSr = 2.301, and ψBa = 2.316. Li, Mg, Ca, Sr, and Ba have lower electron-donating properties than Na. Thus, element A exhibits a stronger electron-withdrawing effect on O than Na, enhancing the O-Na interaction. It is understood that minimizing the electron-donating property of element A is more conducive to enhancing the O-Na interaction.

[0059] In the embodiments of the present application, the value of a represents the doping amount of the doping element A. In the embodiments of the present application, 0<a≤0.1. In some embodiments of the present application, the value of a can be, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments of the present application, 0.01≤a≤0.06. The incorporation of an appropriate amount of doping element A into the sodium layer can, on the one hand, better exhibit an electron-withdrawing effect on the O in the positive electrode material, thereby enhancing the O-Na(A) effect, which is beneficial to improving the structural stability of the positive electrode material under high voltage; on the other hand, it can avoid the occurrence of impurities or element segregation in the synthesis of the positive electrode material; and from the perspective of capacity, the appropriate doping of the doping element A has less effect on the amount of sodium removal, which can better meet the requirement of a maximum sodium removal amount of more than 0.6 for the positive electrode; from the perspective of cost, Na is cheaper than other doping elements, and appropriate doping has a higher performance-to-efficiency ratio.

[0060] In the embodiment of the present application, the element Tm is a transition metal layer element, specifically one or more elements of Ni, Fe, Mn, and Co, and the element Tm forms a transition metal layer with the oxygen element. In the embodiment of the present application, 0.3≤b<1. In some embodiments of the present application, the value of b can be, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9. In some embodiments of the present application, 0.4≤b≤0.9. Controlling the content of the Tm element within a suitable range is beneficial for the positive electrode material to obtain a stable layered structure and maintain the high capacity and other characteristics of the positive electrode material. As a common 3d transition metal active electrode pair, Tm is controlled within a suitable range to provide sufficient charge compensation to meet the demand for sodium removal, that is, to maintain capacity. And as the main element of the material, Tm is within a suitable content range, which is beneficial for the material to obtain a stable layered structure.

[0061] In this application, M 1 , M 2 The introduction of can increase the electron density of coordinated oxygen under high sodium removal of the positive electrode material, thereby strengthening the Na interlayer force.

[0062] In the embodiment of the present application, M 1It is an inert element that does not provide charge compensation, that is, it is an electrochemically inactive element. The doping element M 1 Replace the Tm site in the transition metal layer and form part of the M 1 -O structure. The value of c represents M 1 In some embodiments of the present application, 0<c≤0.6. In some embodiments of the present application, the value of c can be, for example, 0.05, 0.1, 0.15, 0.2, 0.23, 0.25, 0.3, 0.4, 0.5, 0.6. In some embodiments of the present application, 0.05≤c≤0.2. The transition metal Tm layer is doped with the element M 1 Controlling the amount of isotope within a suitable range is beneficial to improving the electron cloud density of O through its electron-donating effect on O, thereby enhancing the O-Na interaction, inhibiting high-voltage phase transition, and improving the structural stability of the positive electrode material under high voltage. Moreover, as a material guest doping element, controlling it within a suitable range is beneficial to the synthesis of pure phase materials, avoiding surface segregation caused by insufficient solid solubility, and at the same time can better ensure the capacity of the positive electrode material.

[0063] In the embodiment of the present application, ψM 1 >ψ 0.6 Tm max , when Tm includes Ni, Fe, Mn and Co at the same time, ψ 0.6 Tm max =1.698. When Tm includes Ni, Mn and Co, ψ 0.6 Tm max =1.657. When Tm includes Ni, Mn and Fe, ψ 0.6 Tm max =1.698. When Tm includes both Ni and Mn, ψ 0.6 Tm max =1.657. In some embodiments of the present application, M 1 It can be one or more elements selected from Li, Ti, Zn, Mg, Sn, Al, Y, La, Nb, and Zr. ψLi = 2.413, ψTi = 1710, ψZn = 2.104, ψMg = 2.206, ψSn = 1.734, ψAl = 1.927, ψY = 2.100, ψLa = 2.113, ψNb = 1.750, ψZr = 1.830. M 1 With a value greater than ψ 0.6 Tm max The feeding property can make M 1 When the amount of sodium removed from the positive electrode material is x, 0.6≤x≤1, the electron-donating effect on O is greater than that of the original transition metal element Tm, and the coordinated O has a higher electron density, which enhances the O-Na-O interaction force. It can be understood that the element M 1The feeding property is as large as possible while satisfying the principle of equivalent substitution, which is more conducive to the enhancement of O-Na related effects.

[0064] In the embodiment of the present application, M 2 Active elements that provide charge compensation, that is, electrochemically active elements, doping elements M 2 Replace the Tm site in the transition metal layer and form part of the M 2 -O structure.M 2 As an active doping element, the feed rate ψ0.6M 2 Bigger M 2 It is more conducive to improving the high pressure stability of the material. The value of d represents M 2 In some embodiments of the present application, 0≤d≤0.2. In some embodiments of the present application, the value of d can be, for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2. In some embodiments of the present application, 0≤d≤0.1. The transition metal Tm layer is doped with the element M 2 The amount of Na is controlled within a suitable range. On the one hand, it is beneficial to increase the electron cloud density of O through its electron donating effect on O, thereby enhancing the O-Na interaction and improving the structural stability of the positive electrode material under high voltage. On the other hand, appropriate doping is beneficial to the synthesis of pure phase, and for cost considerations, appropriate doping has a higher performance-efficiency ratio.

[0065] In some embodiments of the present application, c≥d, that is, in the positive electrode material, M 1 The doping ratio M 2 The doping amount is higher, which is beneficial to better improve the high-voltage stability of the positive electrode material while controlling costs.

[0066] In the embodiment of the present application, ψ 0.6 M 2 >ψ 0.6 Tm max , M 2 It can be one or more elements selected from V, Cr, Ru, Cu, and Ir. 0.6 V=1.745,ψ 0.6 Cr=1.689,ψ 0.6 Ru=1.715,ψ 0.6 Cu=1.847,ψ 0.6 Ir=1.658. ψ 0.6 M 2 >ψ 0.6 Tm max Can make M 2When the sodium removal amount x of the positive electrode material is 0.6≤x≤1, the electron donation effect on O is greater than that of the original transition metal element Tm, and the coordinated O has a higher electron density, which enhances the O-Na-O interaction force. It can be understood that the element M 2 The feeding property is as large as possible while satisfying the principle of equivalent substitution, which is more conducive to the enhancement of O-Na related effects.

[0067] Considering the solid solubility problem, in some embodiments of the present application, M 2 When V is included, the content of V may be less than or equal to 0.1. Controlling the content of V within this range is beneficial to obtaining higher electrochemical performance. 2 When Cu is included, the content of Cu is less than or equal to 0.2. Controlling the content of Cu within this range is beneficial to obtaining higher electrochemical performance.

[0068] In the embodiment of the present application, the particle size D50 of the positive electrode material is 2μm-20μm. In some embodiments, the particle size of the positive electrode material can be 2μm, 4μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm. The positive electrode material of the embodiment of the present application can be spherical, polygonal or lamellar particles, or other morphologies. In some embodiments, the positive electrode material is a flaky particle with a particle size (i.e., sheet diameter) D50 of 2μm-20μm and a particle thickness of 0.1μm-2μm. The particle thickness of the positive electrode material is 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm. Suitable particle size is conducive to the preparation of positive electrode sheets.

[0069] In the embodiment of the present application, the compaction density of the positive electrode material can be 2.8 g·cm -3 -3.2g·cm -3 In some embodiments, the compacted density of the positive electrode material can be 2.8 g·cm -3 , 2.9g·cm -3 , 3.0g·cm -3 , 3.1g·cm -3 , 3.2g·cm -3 The higher compaction density of the positive electrode material is beneficial to the improvement of battery capacity.

[0070] In the embodiment of the present application, the 0.2C charging capacity of the positive electrode material can be 140 mAh g -1 -180mAh·g -1 In some embodiments, the 0.2C charge capacity of the positive electrode material is 145 mAh g -1 -180mAh·g-1 In some embodiments, the 0.2C charge capacity of the positive electrode material is 150 mAh g -1 -160mAh·g -1 The positive electrode material has a high gram capacity, which is beneficial to the improvement of battery capacity.

[0071] In the embodiment of the present application, the crystal structure of the positive electrode material is an α-NaFeO2 hexagonal layered structure. The α-NaFeO2 hexagonal layered structure enables the positive electrode material to have good electrochemical performance.

[0072] The positive electrode material of the embodiment of the present application can be characterized by XRD (X-ray diffraction, X-ray diffraction), EDS (Energy Dispersive Spectrometer, energy spectrometer), EBSD (Electron Backscattered Diffraction, electron backscattered diffraction) and other characterization methods to perform phase analysis, microstructure analysis and other characterization analyses.

[0073] The present invention also provides a method for preparing the positive electrode material, comprising:

[0074] Step 1: According to the molecular formula of the positive electrode material Na 1-na A n+ a [M b M 1 c M 2 d ]O2, sodium source, A source, Tm source, M 1 Source, M 2 The sources are mixed to obtain a mixture;

[0075] Step 2: calcining the mixture obtained in step 1 in an oxygen atmosphere to obtain a positive electrode material.

[0076] In step 1, the sodium source can be a sodium-containing compound, for example, it can be one or more of sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide or sodium hydroxide. The A source can be a compound containing A, for example, it can be one or more of carbonates, nitrates, oxides, peroxides, and hydroxides containing A. The Tm source can be a Tm-containing compound, for example, it can be one or more of metal oxides, metal carbonates, metal nitrates, and metal hydroxides containing Tm. When Tm in the molecular formula includes two or more metal elements, the Tm source can be a co-precipitated compound containing Tm, such as a metal co-precipitated carbonate, a metal co-precipitated hydroxide, etc. For example, the Tm source can be Ni 0.375 Fe 0.25 Mn 0.375 (OH)2. M1 The source can be M 1 Compounds, for example, may contain M 1 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides. 2 The source can be M 2 Compounds, for example, may contain M 2 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides.

[0077] In step 1, sodium source, A source, Tm source, M 1 Source, M 2 The source is mixed, and a wall breaking machine can be used for mixing.

[0078] In step 2, the oxygen atmosphere can be an oxygen atmosphere or an air atmosphere. In some embodiments of the present application, the calcination can be a single-step calcination. In other embodiments of the present application, the calcination can be a two-step calcination or more. The calcined product is cooled to room temperature and then pulverized and sieved to obtain a positive electrode material of the desired particle size.

[0079] When all raw materials are oxides, a one-step calcination can be used. After mixing, solid-phase melt calcination can be performed to obtain the positive electrode material. The one-step calcination can be performed at 800°C-1100°C for 10-20 hours. When all raw materials include non-oxides, a two-step calcination can be performed, wherein a first calcination is performed to decompose the non-oxide raw materials into oxides, followed by a second calcination. The first calcination can be performed at 400°C-500°C for 2-6 hours, and the second calcination can be performed at 800°C-1100°C for 10-20 hours.

[0080] The method for preparing the positive electrode material in the embodiment of the present application has a simple process and does not require complicated steps in the doping process.

[0081] Referring to FIG1 , the present embodiment further provides a positive electrode sheet 10 comprising the positive electrode material described above in the present embodiment. The positive electrode sheet prepared using the positive electrode material described in the present embodiment exhibits high capacity and structural stability, effectively improving the cycling performance of sodium-ion batteries while maintaining their high capacity.

[0082] In the embodiment of the present application, as shown in FIG1 , the positive electrode sheet 10 includes a positive electrode current collector 11 and a positive electrode active layer 12 located on the positive electrode current collector 11. The positive electrode active layer 12 includes a positive electrode active material 121. The positive electrode active material 121 includes the positive electrode material Na 1-na A n+ a [M b M 1 c M2 d ]O2.

[0083] The positive electrode current collector 11 may be a metal foil, such as aluminum foil, gold foil, platinum foil, etc.

[0084] In some embodiments of the present application, the positive electrode active material 121 in the positive electrode active layer 12 is all positive electrode material Na 1-na A n+ a [M b M 1 c M 2 d In some embodiments, the positive electrode active material 121 in the positive electrode active layer 12 includes a positive electrode material Na 1-na A n+ a [M b M 1 c M 2 d ]O2, and also includes other positive electrode active materials. Other positive electrode active materials can be, for example, at least one of other layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanion compounds. In the embodiment of the present application, the layered sodium transition metal oxide can be, for example, sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, abbreviated NFM), the Prussian blue (white) type compound can be, for example, Prussian white (Na2Mn[Fe(CN)6], abbreviated PBA), and the sodium polyanion type compound can be, for example, sodium iron phosphate (NaFePO4, abbreviated NFP).

[0085] In some embodiments of the present application, the mass proportion of the positive electrode active material 121 in the positive electrode active layer 12 is greater than or equal to 92%.

[0086] In the embodiments of the present application, the positive electrode active layer 12 may further include a certain amount of a binder, a conductive agent, and other components. The binder may be, for example, polyvinylidene fluoride (PVDF). The conductive agent may be, for example, amorphous carbon, carbon nanotubes, carbon fibers, graphene, and the like. The above binders and conductive agents are merely illustrative and are not intended to be limiting.

[0087] Referring to Figure 2, the embodiment of the present application also provides a sodium ion battery 100, which includes a positive electrode sheet 10, a negative electrode sheet 20, a separator 30 and an electrolyte 40, wherein the separator 30 is arranged between the positive electrode sheet 10 and the negative electrode sheet 20, and the electrolyte 40 is filled between the positive electrode sheet 10 and the negative electrode sheet 20 and infiltrates the separator 30. The negative electrode sheet 20 includes a negative electrode active material 221, and the negative electrode active material 221 includes a carbon material, wherein, during charging, sodium ions are released from the positive electrode active material 121 of the positive electrode sheet 10, and are embedded in the negative electrode active material 221 of the negative electrode sheet 20 after passing through the electrolyte 40; during discharging, sodium ions are released from the negative electrode active material 221, and are inserted into the positive electrode active material 121 after passing through the electrolyte 40. The sodium ion battery of the embodiment of the present application adopts the positive electrode material Na 1-na A n+ a [Tm b M 1 c M 2 d ]O2 can effectively improve the cycle performance of sodium-ion batteries while maintaining their high capacity.

[0088] In an embodiment of the present application, the negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active layer 22 provided on the surface of the negative electrode current collector 21, wherein the negative electrode current collector 21 can be a metal foil, such as copper foil, aluminum foil, gold foil, platinum foil, etc. The negative electrode material layer includes a negative electrode active material 221, and the negative electrode active material 221 can accept and release sodium ions. In an embodiment of the present application, the negative electrode active material 221 includes a carbon material. In an embodiment of the present application, the carbon material can be one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, and porous carbon materials.

[0089] In the sodium ion battery 100, the electrolyte 40 is the transmission medium when sodium ions are transmitted between the positive electrode sheet 10 and the negative electrode sheet 20. In the embodiment of the present application, the electrolyte 40 includes an organic solvent, an electrolyte salt, and an additive, wherein the electrolyte salt and the additive are both dissolved in the organic solvent.

[0090] In the embodiment of the present application, organic solvent includes but is not limited to one or more of carbonate solvents, ether solvents, and carboxylate solvents.Wherein, carbonate solvents include but are not limited to dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, trifluoromethyl ethylene carbonate, bis (2,2,2-trifluoroethyl) carbonate, (2,2,2-trifluoroethyl) methyl carbonate one or more.Ether solvents include but are not limited to tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis (2,2,2-trifluoroethyl) ether one or more.Carboxylate solvents include but are not limited to one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl difluoroacetate, methyl trifluoroacetate.

[0091] In the embodiment of the present application, the electrolyte salts include but are not limited to NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein m and n are natural numbers. In some embodiments of the present application, the molar concentration of the electrolyte salt in the electrolyte may be 0.01 mol / L-5.0 mol / L.

[0092] In the embodiment of the present application, the additives may include but are not limited to positive electrode film-forming additives, negative electrode film-forming additives, flame retardants, etc.

[0093] In the embodiment of the present application, the diaphragm 30 includes but is not limited to single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP and ceramic-coated PE.

[0094] 3 , the present invention also provides an electrical device 200, which includes the sodium ion battery 100 described above. The electrical device using the sodium ion battery of the present invention has high stability.

[0095] In the embodiment of the present application, the power-consuming device 200 may include an electronic device, an energy storage system, a communication device or a communication base station. As shown in Figure 3, the power-consuming device 200 is an electronic device, which includes a housing 201, and electronic components and a battery 202 housed in the housing 201. The battery 202 supplies power to the electronic components, and the battery 202 includes the sodium ion battery 100 described above in the embodiment of the present application. In the present application, the power-consuming device 200 may be a consumer electronic product, such as a mobile phone, a tablet computer, a desktop computer, a laptop computer, a mobile power supply, a portable computer, a smart screen, a display, an audio device, a vehicle-mounted product, and other wearable or movable electronic devices (such as glasses, watches, bracelets, headphones, etc.), or it may be a vehicle, an energy storage device, a communication device, a base station and other equipment products.

[0096] The embodiments of the present application are further described below with reference to a number of embodiments.

[0097] Example 1

[0098] Na 0.94 Ca 0.03 Ni 0.5 Ti 0.5 Preparation of O2 layered cathode materials:

[0099] Na2CO3, CaO, NiO, and TiO2 are added to a wall breaker in a stoichiometric ratio for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. Air is passed through the entire calcination process. The calcination program is set to a heating rate of 5°C / min. After heating to 1000°C, it is kept warm for 15 hours and cooled to room temperature. After discharging, the material is crushed by a pulverizer and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0100] Positive electrode preparation:

[0101] The obtained layered positive electrode material, conductive additive SP, and binder PVDF were mixed in weight proportions of 92 parts, 4 parts, and 4 parts, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry was then evenly coated on a carbon-coated aluminum foil, dried, and sliced ​​to obtain a positive electrode sheet.

[0102] Sodium ion battery preparation:

[0103] The prepared positive electrode sheet and the metallic sodium negative electrode were assembled into a sodium ion battery, and a carbonate electrolyte (1M NaClO4 dissolved in PC+5% FEC solution) was selected as the electrolyte.

[0104] Example 2

[0105] Na 0.94 Ca 0.03 Ni 0.4 Ti 0.5 Zn 0.1Preparation of O2 layered cathode materials:

[0106] Na2CO3, CaO, NiO, TiO2, and ZnO were added to a wall breaker in a stoichiometric ratio for mixing. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire calcination process. The calcination program was set to a heating rate of 5°C / min. After heating to 1000°C, the temperature was kept for 15 hours, cooled to room temperature, and crushed by a grinder after discharge, and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0107] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0108] Example 3

[0109] Na 0.94 Ca 0.02 Li 0.02 Ni 0.5 Ti 0.5 Preparation of O2 layered cathode materials:

[0110] Na2CO3, CaO, Li2CO3, NiO, and TiO2 are added to a wall breaker in a stoichiometric ratio for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. Air is passed through the entire calcination process. The calcination program is set to a heating rate of 5°C / min. After heating to 1000°C, it is kept warm for 15 hours and cooled to room temperature. After discharging, the material is crushed by a pulverizer and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0111] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0112] Example 4

[0113] Na 0.94 Ca 0.03 Ni 0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0114] Take Na2CO3, CaO, Ni according to the stoichiometric ratio 0.33 Fe 0.33 Mn 0.33(OH)2, CuO, and TiO2 are added to a wall breaker for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0115] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0116] Example 5

[0117] Na 0.94 Mg 0.03 Ni 0.3 Fe 0.3 Mn 0.3 Li 0.067 Ti 0.133 Preparation of O2 layered cathode materials:

[0118] Take Na2CO3, MgO, Ni according to the stoichiometric ratio 0.33 Fe 0.33 Mn 0.33 (OH)2, Li2CO3, and TiO2 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0119] Figure 4 shows the cathode material Na provided in Example 5 of this application. 0.94 Mg 0.03 Ni 0.3 Fe 0.3 Mn 0.3 Li 0.067 Ti 0.133 EDS element distribution diagram of O2. It can be seen from the element distribution diagram in Figure 4 that the obtained positive electrode material contains Na, Mg, Ni, Fe, Mn, Ti, and O.

[0120] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0121] Example 6

[0122] Na 0.94 Li 0.06 Ni0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0123] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni 0.33 Fe 0.33 Mn 0.33 (OH)2, CuO, and TiO2 are added to a wall breaker for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0124] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0125] Example 7

[0126] Na 0.94 Mg 0.03 Ni 0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0127] Take Na2CO3, MgO, Ni according to the stoichiometric ratio 0.33 Fe 0.33 Mn 0.33 (OH)2, CuO, and TiO2 are added to a wall breaker for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0128] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0129] Example 8

[0130] Na 0.94 Mg 0.03 Ni 0.3 Fe 0.3 Mn0.3 Zn 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0131] Take Na2CO3, MgO, Ni according to the stoichiometric ratio 0.33 Fe 0.33 Mn 0.33 (OH)2, ZnO, and TiO2 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours, and then naturally cooled. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0132] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0133] Example 9

[0134] Na 0.94 Mg 0.03 Ni 0.3 Fe 0.2 Mn 0.3 Al 0.05 Ti 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0135] Take Na2CO3, MgO, Ni according to the stoichiometric ratio 0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and Al2O3 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours, and then naturally cooled. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0136] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0137] Example 10

[0138] Na 0.94 Ca 0.03 Ni 0.3 Fe 0.2 Mn 0.3Co 0.05 Ti 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0139] Take Na2CO3, CaO, Ni according to the stoichiometric ratio 0.375 Fe 0.25 Mn 0.375 (OH)2, Co2O3, TiO2, and Li2CO3 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours, and then naturally cooled. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0140] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0141] Example 11

[0142] Na 0.94 Li 0.06 Ni 0.3 Fe 0.2 Mn 0.3 V 0.05 Ti 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0143] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni 0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and V2O5 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. The temperature is then naturally lowered. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0144] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0145] Example 12

[0146] Na 0.94 Ca 0.03 Ni 0.3 Fe 0.2Mn 0.3 Cr 0.05 Ti 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0147] Take Na2CO3, CaO, Ni according to the stoichiometric ratio 0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and Cr2O3 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. The temperature is then naturally lowered. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0148] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0149] Example 13

[0150] Na 0.94 Ca 0.03 Ni 0.3 Fe 0.2 Mn 0.3 Ru 0.05 Sn 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0151] Take Na2CO3, CaO, Ni according to the stoichiometric ratio 0.375 Fe 0.25 Mn 0.375 (OH)2, SnO2, Li2CO3, and RuO2 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. The temperature is then naturally lowered. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0152] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0153] Example 14

[0154] Na 0.93 Li 0.07 Ni 0.3Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0155] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni 0.33 Fe 0.33 Mn 0.33 (OH)2, CuO, and TiO2 are added to a wall breaker for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0156] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0157] Example 15

[0158] Na 0.94 Ca 0.03 Ni 0.4 Mn 0.4 Zn 0.1 Ti 0.1 Preparation of O2 layered cathode materials:

[0159] Na2CO3, CaO, NiO, MnO2, TiO2, and ZnO were added to a wall breaker in a stoichiometric ratio for mixing. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire calcination process. The calcination program was set to a heating rate of 5°C / min. After heating to 1000°C, the temperature was kept for 15 hours, cooled to room temperature, and crushed by a grinder after discharge, and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0160] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0161] Example 16

[0162] Na 0.94 Li 0.06 Ni 0.3 Fe 0.2 Mn 0.3 V 0.1 Ti 0.067 Li 0.033 Preparation of O2 layered cathode materials:

[0163] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and V2O5 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. The temperature is then naturally lowered. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0164] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0165] Example 17

[0166] Na 0.94 Li 0.06 Ni 0.3 Fe 0.2 Mn 0.3 V 0.11 Ti 0.06 Li 0.03 Preparation of O2 layered cathode materials:

[0167] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni 0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and V2O5 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. The temperature is then naturally lowered. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0168] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0169] Example 18

[0170] Na 0.94 Mg 0.03 Ni 0.3 Fe 0.2 Mn 0.27 Al 0.08 Ti 0.1 Li 0.05 Preparation of O2 layered cathode materials:

[0171] Take Na2CO3, MgO, Ni according to the stoichiometric ratio 0.375 Fe 0.25 Mn 0.375 (OH)2, TiO2, Li2CO3, and Al2O3 are added to a wall breaker for mixing. The mixed precursors are transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours, and then naturally cooled. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0172] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0173] Example 19

[0174] Na 0.95 Li 0.05 Ni 0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0175] According to the stoichiometric ratio, Na2CO3, Li2CO3, Ni 0.33 Fe 0.33 Mn 0.33 (OH)2, CuO, and TiO2 are added to a wall breaker for mixing. The mixed precursor is transferred to a sagger and then placed in an atmosphere furnace for calcination. The calcination is divided into two stages with air. The heating rate is set at 3°C / min for the first calcination process, and after rising to 450°C, it is kept warm for 6 hours and cooled to room temperature. The second mixing is then carried out in a wall breaker and the second calcination is carried out again. The heating rate is set at 5°C / min for the second calcination process, and after rising to 1000°C, it is kept warm for 15 hours. It is then cooled naturally. After discharge, the material is crushed by a grinder and passed through a 200-mesh sieve to obtain the positive electrode material.

[0176] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0177] Comparative Example 1

[0178] Preparation of NaNiO2 layered cathode materials:

[0179] Na2O2 and NiO were taken in a stoichiometric ratio, added to a wall breaker for mixing, taken out after mixing, transferred to a sagger, and calcined in an oxygen atmosphere in an atmosphere furnace. The calcination program was set to a heating rate of 5°C / min. After rising to 800°C, the temperature was kept for 12 hours. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. The whole process was calcined with air. The calcination program was set to a heating rate of 5°C / min. After rising to 1000°C, the temperature was kept for 15 hours. The material was cooled to room temperature, and the material was crushed by a grinder after discharge and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0180] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0181] Comparative Example 2

[0182] Na 0.94 Ca 0.03 Preparation of NiO2 layered cathode materials:

[0183] Na2O2, CaO, and NiO were added to a wall breaker according to the stoichiometric ratio for mixing, and then removed after completion. The mixed precursor was transferred to a sagger and then calcined in an atmosphere furnace with oxygen flowing throughout the calcination process. The calcination program was set to a heating rate of 5°C / min, and after heating to 750°C, the temperature was maintained for 15 hours, cooled to room temperature, and crushed in a pulverizer and passed through a 200-mesh screen to obtain the positive electrode material.

[0184] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0185] Comparative Example 3

[0186] Nani 0.5 Ti 0.5 Preparation of O2 layered cathode materials:

[0187] Accurately weigh Na2CO3, NiO, and TiO2 according to the stoichiometric ratio and add them into the wall breaking machine for mixing, and take them out after mixing.

[0188] The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire process. The calcination program was set to a heating rate of 5°C / min. After rising to 1000°C, it was kept warm for 15 hours. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire process. The calcination program was set to a heating rate of 5°C / min. After rising to 1000°C, it was kept warm for 15 hours. It was cooled to room temperature. After discharging, the material was crushed by a grinder and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0189] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0190] Comparative Example 4

[0191] Nani0.4 Ti 0.5 Zn 0.1 Preparation of O2 layered cathode materials:

[0192] Na2CO3, NiO, TiO2, and ZnO were accurately weighed according to the stoichiometric ratio and added to the wall breaking machine for mixing. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire calcination process. The calcination program was set to a heating rate of 5°C / min. After heating to 1000°C, it was kept warm for 15 hours and cooled to room temperature. After discharging, it was crushed by a pulverizer and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0193] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0194] Comparative Example 5

[0195] Nani 0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 Preparation of O2 layered cathode materials:

[0196] Na2CO3, NiO, Fe2O3, MnO2, CuO, and TiO2 were accurately weighed according to the stoichiometric ratio and added to the wall breaking machine for mixing. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire calcination process. The calcination program was set to a heating rate of 5°C / min. After heating to 1000°C, it was kept warm for 15 hours and cooled to room temperature. After discharging, the material was crushed by a pulverizer and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0197] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0198] Comparative Example 6

[0199] Na 0.94 Ca 0.03 Ni 0.5 Mn 0.5 Preparation of O2 layered cathode materials:

[0200] Na2CO3, CaO, NiO, TiO2, and ZnO were added to a wall breaker in a stoichiometric ratio for mixing. The mixed precursor was transferred to a sagger and then placed in an atmosphere furnace for calcination. Air was passed through the entire calcination process. The calcination program was set to a heating rate of 5°C / min. After heating to 1000°C, the temperature was kept for 15 hours, cooled to room temperature, and crushed by a grinder after discharge, and passed through a 200-mesh sieve to obtain a layered positive electrode material.

[0201] The preparation of the positive electrode sheet and the sodium ion battery was the same as in Example 1.

[0202] Comparative Example 7

[0203] The commercial cathode material NaNi 0.33 Fe 0.34 Mn 0.33 O2 The positive electrode sheet and sodium ion battery were prepared using the method of Example 1.

[0204] The maximum sodium removal amount before phase transition, phase transition capacity, and 300-cycle capacity retention of the sodium ion batteries of Examples 1 to 19 and Comparative Examples 1 to 7 were measured. The results are shown in Table 1.

[0205] The maximum amount of sodium removed before the phase change reflects the maximum reversible capacity of the material before the irreversible phase change, which is equal to the ratio of the capacity before the charging phase change platform to the theoretical capacity. For example, for NaNiO2, assuming that the capacity before the high-voltage phase change platform is 140mAh / g, and the theoretical capacity of NaNiO2 is 235.7mAh / g, it can be calculated that the maximum amount of sodium removed before the phase change = 140 / 235.7 = 0.59. Test method: At 0.2C, the first charge is carried out at a current density of 32mA / g to obtain the first charge curve of the material. Two slopes are drawn for the curves before and after the phase change, and the sodium removal corresponding to the intersection is the maximum sodium removal before the phase change.

[0206] Phase change capacity reflects the degree of irreversible phase change. The greater the phase change capacity, the greater the irreversible capacity. Testing method: Perform the first charge at 0.2C and a current density of 32mA / g. The difference between the first charge capacity and the capacity corresponding to the material's maximum sodium removal is the phase change capacity.

[0207] The 300-cycle capacity retention rate is the ratio of the battery's 300-cycle capacity to its first-cycle capacity. Test method: Calculate the capacity retention rate after 300 charge-discharge cycles at 1C and a current density of 160 mAh / g.

[0208] FIG5 is a curve diagram of the maximum sodium removal amount before phase change of the positive electrode material provided in Example 9 of the present application; as shown in FIG5 , the maximum sodium removal amount before phase change of the positive electrode material of Example 9 is 0.63.

[0209] FIG6 is a phase change capacity curve diagram of the positive electrode material provided in Example 9 of the present application; As can be seen from FIG6 , the phase change capacity of the positive electrode material of Example 9 is 18.

[0210] FIG7 is a curve diagram of the maximum sodium removal amount before phase change of the positive electrode material provided in Comparative Example 7 of the present application; as shown in FIG7 , the maximum sodium removal amount before phase change of the positive electrode material of Comparative Example 7 is 0.58.

[0211] FIG8 is a phase change capacity curve diagram of the positive electrode material provided in Comparative Example 7 of the present application; As can be seen from FIG8 , the phase change capacity of the positive electrode material of Comparative Example 7 is 34.

[0212] Table 1

[0213] It can be seen from Table 1 that compared with the positive electrode material NaNiO2 of comparative example 1, the positive electrode materials of Examples 1 to 17 of the present application are co-doped with the sodium layer and the transition metal layer, and their maximum sodium removal amount before phase change is improved, and the phase change capacity is significantly reduced, that is, the high-voltage phase change stability is improved, and at the same time, the 300-cycle capacity retention rate is significantly improved.

[0214] Compared with the positive electrode material NaNiO2 of Comparative Example 1, the positive electrode material Na 0.94 Ca 0.03 NiO2, and the positive electrode material NaNi of Comparative Example 3 0.5 Ti 0.5 O2, the positive electrode materials of Examples 1 to 3 of the present application, by co-doping with the sodium layer and the transition metal layer, have an increased maximum sodium removal amount before phase transition, and a significant decrease in phase transition capacity, that is, the high-voltage phase transition stability is improved, and the 300-cycle capacity retention rate is significantly improved. This is mainly due to the multi-element co-doping of the sodium layer and the transition metal layer, which fully utilizes the synergistic effect between the elements, thereby significantly improving the electrochemical performance of the positive electrode material.

[0215] Compared with the positive electrode material NaNi of Comparative Example 4 0.4 Ti 0.5 Zn 0.1 O2, the positive electrode material Na of Example 2 of the present application 0.94 Ca 0.03 Ni 0.4 Ti 0.5 Zn 0.1 O2, through sodium layer doping, its maximum sodium removal before phase change is improved, the phase change capacity is significantly reduced, and the 300-cycle capacity retention rate is significantly improved.

[0216] Compared with the positive electrode material NaNi of Comparative Example 5 0.3 Fe 0.3 Mn 0.3 Cu 0.05 Ti 0.05 O2, the positive electrode materials of Examples 4, 6, 7, 14, and 19 of the present application are co-doped with a sodium layer and a transition metal layer, and their maximum sodium removal amount before phase change is significantly improved, the phase change capacity is significantly reduced, and the 300-cycle capacity retention rate is significantly improved.

[0217] Compared with the positive electrode material Na 0.94 Ca 0.03 Ni 0.5 Mn 0.5O2. The positive electrode material of Example 15 of the present application is co-doped with a sodium layer and a transition metal layer, and its maximum sodium removal amount before phase change is significantly improved, the phase change capacity is significantly reduced, and the 300-cycle capacity retention rate is significantly improved.

[0218] Compared with the positive electrode material NaNi of Comparative Example 7 0.33 Fe 0.34 Mn 0.33 O2, the positive electrode materials of Examples 4-14 and Examples 16-19 of the present application are co-doped with a sodium layer and a transition metal layer, and their maximum sodium removal amount before phase change is significantly improved, the phase change capacity is significantly reduced, and the 300-cycle capacity retention rate is significantly improved.

[0219] As shown in Figures 5 to 8, compared with the positive electrode material NaNi of Comparative Example 7 0.33 Fe 0.34 Mn 0.33 O2, the positive electrode material Na of Example 9 of the present application 0.94 Mg 0.03 Ni 0.3 Fe 0.2 Mn 0.3 Al 0.05 Ti 0.1 Li 0.05 O2, by doping the sodium layer with an appropriate amount of magnesium and the transition metal layer with an appropriate amount of Al, Ti, and Li, the maximum sodium removal amount of the positive electrode material before the phase change is significantly increased, and the phase change capacity is significantly decreased.

[0220] Comparing Examples 1 to 3, it can be seen that the positive electrode material Na 0.94 Ca 0.03 Ni 0.4 Ti 0.5 Zn 0.1 O2 is doped with multiple elements through the transition metal layer, and its performance is improved compared with the positive electrode material of Example 1; the positive electrode material Na of Example 3 0.94 Ca 0.02 Li 0.02 Ni 0.5 Ti 0.5 O2 is doped with multiple elements through the sodium layer, and its performance is improved compared with the positive electrode material of Example 1.

[0221] It should be understood that the first, second and various numerical numbers involved in this document are only distinguished for the convenience of description and are not intended to limit the scope of this application.

[0222] In this application, "and / or" describes the relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the related objects are in an "or" relationship.

[0223] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0224] Likewise, "at least one" means one or more, and "a plurality of" means two or more.

[0225] In this application, “-” represents a range value, including the endpoint values ​​at both ends. For example, the value of a can be 0.5-15, which means that the value of a can be between 0.5 and 15, and includes the endpoint values ​​0.5 and 15.

[0226] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

Claims

1. A positive electrode material, characterized in that: The molecular formula of the positive electrode material is Na 1-na A n+ a [Tm b M 1 c M 2 d ]O2, wherein A is one or more alkali metal or alkaline earth metal elements with a power feeding property ψA satisfying 0.9ψNa≤ψA<ψNa; Tm is a combination of one or more elements of Fe, Mn, Co and Ni, M 1 is the feeding characteristic ψM 1 Satisfy ψM 1 >ψ 0.6 Tm max One or more metal elements, and M 1 M is an inert element that does not provide charge compensation. 2 The feeding characteristic ψ 0.6 M 2 Satisfy ψ 0.6 M 2 >ψ 0.6 Tm max One or more metal elements, and M 2 An active element that provides charge compensation; 0<a≤0.1, 0.3≤b<1, 0<c≤0.6, 0≤d≤0.2, b+c+d=1, and the values ​​of a, b, c, d enable the positive electrode material to maintain charge balance; Among them, ψA=χO-χA; ψM 1 =χO-χM 1 , χO is the effective electronegativity of O, χA is the effective electronegativity of A, χM 1 M 1 The effective electronegativity of 0.6 Tm max is the maximum chargeability of Tm when the amount of sodium removal of the positive electrode material is greater than or equal to 0.6, where ψ 0.6 Tm = ψiniTm-0.6*(ψiniTm-ψendTm), ψiniTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 0, and ψendTm is the power feeding property of Tm when the amount of sodium removal of the positive electrode material is 1; ψ 0.6 M 2 =ψiniM 2 -0.6*(ψiniM 2 -ψendM 2 ), ψiniM 2 When the amount of sodium removed from the positive electrode material is 0, M 2 The feeding property, ψendM 2 When the amount of sodium removed from the positive electrode material is 1, M 2 The feeding property.

2. The positive electrode material according to claim 1, characterized in that 0.01≤a≤0.06。 3. The positive electrode material according to claim 1 or 2, characterized in that 0.4≤b≤0.9。 4. The positive electrode material according to any one of claims 1 to 3, characterized in that 0.05≤c≤0.2。 5. The positive electrode material according to any one of claims 1 to 4, characterized in that 0≤d≤0.1。 6. The positive electrode material according to any one of claims 1 to 5, characterized in that The A is selected from one or more elements of Li, Mg, Ca, Sr, and Ba.

7. The positive electrode material according to any one of claims 1 to 6, characterized in that The M 1 One or more elements selected from Li, Ti, Zn, Mg, Sn, Al, Y, La, Nd, and Zr.

8. The positive electrode material according to any one of claims 1 to 7, characterized in that The M 2 One or more elements selected from V, Cr, Ru, Cu, and Ir.

9. The positive electrode material according to any one of claims 1 to 8, characterized in that The positive electrode material is in the form of spherical, polygonal or lamellar particles, and the particle size D50 is 2 μm-20 μm.

10. The positive electrode material according to any one of claims 1 to 9, characterized in that The compaction density of the positive electrode material is 2.8 g·cm -3 -3.2g cm -3 .

11. The positive electrode material according to any one of claims 1 to 10, characterized in that The gram capacity of the positive electrode material is 140 mAh g -1 -180mAh g -1 .

12. The positive electrode material according to any one of claims 1 to 11, characterized in that The crystal structure of the positive electrode material is an α-NaFeO2 hexagonal layered structure.

13. A method for preparing the positive electrode material according to any one of claims 1 to 12, characterized in that: include: According to the molecular formula of the positive electrode material Na 1-na A n+ a [Tm b M 1 c M 2 d ]O2, sodium source, A source, Tm source, M 1 Source, M 2 The sources are mixed to obtain a mixed material; The mixed material is calcined in an oxygen atmosphere to obtain a positive electrode material.

14. The preparation method according to claim 13, characterized in that: The sodium source includes a sodium-containing compound, and the sodium-containing compound includes one or more of sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide and sodium hydroxide; the A source includes an A-containing compound, and the A-containing compound includes one or more of carbonates, nitrates, oxides, peroxides and hydroxides containing A; the Tm source includes a Tm-containing compound, and the Tm-containing compound includes one or more of metal oxides, metal carbonates, metal nitrates and metal hydroxides containing Tm; the M 1 Sources include M 1 Compound, the compound containing M 1 Compounds including M 1 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides; the M 2 Sources include M 2 Compound, the compound containing M 2 Compounds including M 2 One or more of carbonates, nitrates, oxides, peroxides, and hydroxides.

15. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 12.

16. The positive electrode sheet according to claim 15, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on the positive electrode current collector, and the positive electrode active layer includes the positive electrode material.

17. A sodium ion battery, characterized in that: The sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet comprises the positive electrode sheet according to claim 15 or 16.

18. An electrical equipment, characterized in that: The electrical equipment comprises the sodium ion battery according to claim 17.

19. The electrical equipment according to claim 18, characterized in that the electrical equipment comprises an electronic device, an energy storage system, a communication device or a communication base station.

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